This invention relates to force feedback hand controllers, particularly to six degree of freedom hand controllers with three degree of freedom rotational handles.
Many attempts have been made to design a realistic force-reflecting master hand controller. These may be organized into serial devices, parallel devices, and hybrid constructions.
The present invention falls under the class of serial device; known examples are listed here:
Serial master devices are produced by Sarcos Research Corporation and CyberNet, among others. The Sarcos device is described by Jacobsen et al (1989) as a ten degree of freedom exoskeleton designed to match the user""s arm. It is primarily used to control a slave arm that is kinematically similar to the master arm.
CyberNet""s PERforce device is described in Burdea [1996]. It has six linkages connected by rotational joints, terminating in an aircraft style joystick. McAffee et al [1993] describe the CyberNet system as a force reflecting hand controller composed of connected linkagesxe2x80x94a group of three for translation, carrying a group of three for rotation. This system makes use of cables and pulleys to transmit forces to the joints, and to carry joint position information to sensors at the base. Sensors arrayed in this manner can lead to instabilities because of delays in sensor signal transmission, owing to stretching of the cables and axial movement on the pulleys.
CyberNet personnel later invented a different system [Jacobus et al, 1995]. This hand controller consists of a three-axis prismatic base translation stage, surmounted by a three-axis rotary stage. Springs are positioned to counteract earth""s gravity, allowing the translation stage to float. Low-ratio gears assemblies connect each axis to DC motors mounted in the stage supporting that axis. Back-drivabilityxe2x80x94the ability to push the handle against the supporting, driving mechanismxe2x80x94is reduced by the presence of gears.
Yokoi et al [1994] also presents a hand controller using three prismatic actuators for translation surmounted by three rotary actuators for orientation.
Massie and Salisbury [1994] describe their PHANToM device, which consists of instrumented gimbals mounted on a balanced four-bar mechanism. The four-bar is motorized, whereas the gimbals are a passive assembly. The PHANToM differs from the other serial devices just described in that only three of the six axes are motorized.
Likewise, Rosenberg et al [1996] outline a three-degree of freedom device that makes use of springs or counterweights to balance against gravity, and a force generator to present forces to the user.
Parallel devices are as follows:
Cleary and Brooks [1993] present a 6-DOF device combining three 2-DOF linkages. Iwata [1990] built a 9-DOF device that provides 6-DOF motion to the hand and 1 -DOF motion to 3 sets of fingers. Iwata [1 993] also experimented with a 6-DOF haptic pen positioned by two 3-DOF manipulators. Long and Collins [1992] report a 6-DOF joystick with three parallel pantograph linkages. Millman and Colgate [1991] describe a haptic probe with three active translational degrees of freedom and three passive rotational degrees of freedom. A 4-DOF device using only rotary actuators is presented in Kotoku et al [1992]. Millman et al [1993] describe a 4-DOF (3 translation, 1 rotation) joystick. A 2-DOF five-bar linkage with a horizontal planar workspace is optimized in Hayward et al [1994]. Kelley and Salcudean [1994] present a 2-DOF planar positioning device actuated by linear voice coils. Finally, Vertut [1977] presents an historical survey of earlier hand controllers, articulated arms, and exoskeletons.
A hybrid serial parallel device is described by Stocco and Salcudean (1996). This device, the Twin Elbow, makes use of two five-bar linkages to drive either end of a platform, with a motorized serial linkage to rotate the platform around an axis defined by its endpoints. Hayward et al [1997] describe a parallel device installed in the distal stage of a six degree of freedom hand controller, carried by a balanced serial translation stage.
Burdea, G. C. [1996]. Force and Touch Feedback for Virtual Reality. John Wiley and Sons. New York, p. 82.
Cleary K. and Brooks T. [1993], xe2x80x9cKinematic Analysis of a Novel 6-DOF Parallel Manipulatorxe2x80x9d, IEEE International Conference on Robotics and Automation, Atlanta, Ga., pp. 708-713, 1993.
Hayward, V. [1994], J. Choksi, G. Lanvin, C. Ramstein, xe2x80x9cDesign and multi-objective optimization of a linkage for a haptic interfacexe2x80x9d, Proc. ARK ""94, 4th Int. Workshop on Advances in Robot Kinematics (Ljubliana, Slovenia), June 1994.
Hayward V., Gregario P, Astley O., Greenish S., Doyon M., Lessard L., McDougall J., Sinclair I., Boelen S., Chen X. Demers J.-P. and Poulin J. xe2x80x9cFreedom 7: A High Fidelity Seven Axis Haptic Device with Application to Surgical Trainingxe2x80x9d, ISER""97, Barcelona, Spain, Jun. 15-18, 1997.
Iwata H. [1990], xe2x80x9cArtificial Reality with Force-feedback: Development of Desktop Virtual Space with Compact Master Manipulatorxe2x80x9d, SIGGRAPH, Dallas, Tex., Vol. 24, No. 4, pp. 165-170, Aug. 6-10, 1990.
Iwata H. [1993], xe2x80x9cPen-based Haptic Virtual Environmentxe2x80x9d, IEEE International Symposium Conference on Robotics and Automation, 1993.
Jacobsen S, Iversen E., Davis C., Poter D., and McLain T. [1989]. xe2x80x9cDesign of a multiple degree of freedom, force-reflective hand master/slave with a high mobility wristxe2x80x9d. Proc. ANS/IEEE/SMC 3rd Topical Meeting on Robotics and Remote Systems, ANSI, New York, March 1989.
Jacobus, C. J, Riggs A. J., and Taylor, M. J. Method and system for providing a tactile virtual reality and manipulator defining an interface device therefor, U.S. Pat. No. 5,459,382, issued Oct. 17, 1995.
Kelley A. J. and Salcudean S. E. [1994], xe2x80x9cThe Development of a Force-Feedback Mouse and its Integration into a Graphical User Interfacexe2x80x9d, Proc. Int. Mech. Eng. Congress and Exposition, Chicago, Ill., DSC-Vol 55-1, pp. 287-294, Nov. 6-11, 1994.
Kotoku T., Komoriya K. and Tanie K. [1992]. xe2x80x9cA force display system for virtual environments and its evaluationxe2x80x9d, IEEE Int. Workshop on Robot and Human Commun., Tokyo, Japan., pp. 246-251, Sep. 1-3, 1992.
Long G. and Collings C. [1992], xe2x80x9cA Pantograph Linkage Parallel Platform Master Hand Controller for Force-Reflectionxe2x80x9d, IEEE International Conference on Robotics and Automation, 1992.
Massie T. and Salisbury K. [1994], xe2x80x9cThe PHANToM Haptic Interface: a Device for Probing Virtual Objectsxe2x80x9d, ASME Winter Annual Meeting, DSC-Vol 55-1, ASME, New York, pp. 295-300.
McAffee D. A., Snow E. R., Townsend W. T. [1993]. xe2x80x9cForce reflecting hand controllerxe2x80x9d, U.S. Pat. No. 5,193,963, issued Mar. 16, 1993.
Millman P, Stanley M. and Colgate J. [1993], xe2x80x9cDesign of a High Performance Haptic Interface to Virtual Environmentsxe2x80x9d, IEEE International Conference on Robotics and Automation, 1993.
Millman, P. A. and J. E. Colgate [1991], xe2x80x9cDesign of a four degree-of-freedom force-reflecting manipulandum with a specified force/torque workspacexe2x80x9d, Proc. IEEE Int. conf. Robotics and Auto. (Sacramento, Calif., pp. 1488-1493, Apr. 9-11, 1991.
Rosenberg, L. B. and Jackson, B. G. Electromechanical human-computer interface with force feedback, U.S. Pat. No. 5,576,727, issued Nov. 19, 1996.
Stocco, L and Salcudean, S. E. xe2x80x9cA Coarse-Fine Approach to Force-Reflecting Hand Controller designxe2x80x9d. IEEE International Conference on Robotics and Automation, Minneapolis, Minn. Apr. 22, 1996.
Vertut, J. [1977]. xe2x80x9cControl of master slave manipulators and force feedbackxe2x80x9d, Proc. 1977 Joint Auto. Control Conf., 1997.
Yokoi H. [1994], Yamashita J., Fukui Y. and Shimoho M., xe2x80x9cDevelopment of 3D-Input Device for Virtual Surface Manipulationxe2x80x9d, IEEE International Workshop on Robot and Human Communication, 1994.
This invention is the distal mechanism, (handle stage or rotational stage) of a six-degree of freedom force-feedback hand controller. It provides three degrees of freedom of rotational motion for the handle. The handle may consist of any shape suitable for gripping with the hand, such as an elongated cylinder, or a scissors mechanism; different handles may be interchangeable.
The distal mechanism is rigidly attached to a base that may be moveable, that is, it may be a means for providing three degree of freedom translation motion. One embodiment of the moveable base is a balanced, serial mechanism. In the present invention, this moveable base consists of a four-bar coupled to 2-DOF gimbals. Heavy counterweights are used near the axis of movement of the base, in order to minimize inertia. (Inertia of a mass varies as the square of the distance from the axis; by placing heavy mass closer to the axis, inertia is reduced compared to a lighter balancing mass place farther from the axis.) Counterweights are inherently more reliable than springs, which can break and/or vary in spring constant because of metal fatigue.
The distal mechanism consists of a first stage, a second stage and a third stage. The first stage supports the second and third stages, and the second stage supports the third stage. The first stage is mounted on the moveable base, and the third stage carries the handle. The first stage has a first stage axis of rotation, the second stage has a second stage axis of rotation, and the third stage has a third stage axis of rotation. The first, second and third axes of rotation cross one another at an axis crossing point, forming a three degree of freedom spherical mechanism.
The handle has an axis that is coincident with the axis of the third stage. The handle is axially connected to a handle shaft that turns in a handle shaft support bearing assembly. The handle shaft passes through the axis crossing point. The second stage houses the handle shaft support bearing assembly, and also a second stage bearing assembly that permits rotation of the second stage about the second stage axis of rotation. The body of the second stage bearing assembly is fixedly attached to a second stage support assembly that is in turn fixedly attached to a first stage shaft. The first stage shaft is supported by a first stage shaft support bearing assembly that permits rotation about the first stage axis. The body of the first stage support bearing assembly is fixedly attached to the moveable platform.
Each stage is connected fixedly to a drive pulley, with an axis coincident with the axis of rotation of its respective stage. Torque is transmitted by means of tendons from three rotary motors to the drive pulleys on the three stages. The three motors are positioned at the base of the hand controller. The tendons pass from the motor along idlers positioned in the translation stage joints, to the distal mechanism. In the distal mechanism, idlers direct the tendons to the drive pulley on each stage. Typically, the tendon is wrapped twice around each drive pulley, and secured to a tying point on the drive pulley. The two ends of each tendon meet at this point.
The tendon for a given stage is wrapped several times around a capstan on the motor. The middle loop on the capstan is also passed around an idler pulley attached to a spring-loaded assembly with a single degree of freedom, positioned in such a way that the spring, acting on the single degree of freedom, provides tension to the tendon.
Each stage is also connected fixedly to the shaft of a magneto-resistance rotary angle sensor. The axis of the sensors is coincident with the rotary axis of its respective stage. In addition, a fourth sensor is used to detect the rotational angle of the third stage. This fourth sensor is mounted on an idler which redirects the tendon path to the axis of the fourth stage. Having two sensors extends the range of the third stage handle rotation about its axis from the 110-degree limitation of the rotary sensor to a full 360 degrees.
The main object of the device is to serve as the rotation (or distal) stage, mounted at the end of a translation stage in a six-degree of freedom force feedback hand controller. The handle roll, pitch and yaw angles are sensed in the mechanism, and transmitted to a computer system, which then returns appropriate torque to be applied to the handle""s roll, pitch and yaw. The user, grasping the handle, can control a portion of a computer simulation, and experience forces generated in the computer simulation.
High-resolution magneto-resistance sensors are used for angular measurement. These non-contact sensors have advantages over potentiometers, in terms of smooth response, low friction and low noise levels; compared to optical encoders, they are lighter and less expensive; compared to RVDTs (rotary variable differential transducers) they have simpler control electronics and consequently a lower price.
The device uses polymer tendons to provide driving force, with motors situated on the base. These tendons transmit the drive forces in the most efficient manner, since they are lightweight and minimally extensible. Other flexible tendons may be used. Polymer tendons have less bending resistance than metallic cables, and so offer minimal resistance to motion.
There are no gears. Tendons are used to connect the three axes to the motors, permitting maximum back-drivability. Gears reduce back-drivability by operating primarily in one direction, from the motor toward the load.
Having the sensors incorporated directly into the distal stage allows for an immediate reading on the position of the user""s hand, by means of the handle. Sensors located some distance away, along the tendon path, suffer from lag and inaccuracy introduced by slackness in the tendon, caused in turn by movement of the tendon on the idler pulleys or by imperfections in the pulley bearings and supports. The accuracy of the reading makes the control loop more stable, and allows for very robust calibration of the handle rotational position.
The serial nature of the mechanism means a simpler forward kinematics and static force analysis compared to a parallel mechanism. Computationally, it provides a much simpler coupling between the corresponding degrees of freedom.
This device is especially compact, so that weight is reduced while avoiding the use of tiny parts (e.g. jewel bearings), thereby making it mechanically robust. Reduced weight implies less inertia in the movement and an improved response to a given torque, enabling higher virtual stiffness.
The mechanism can be upgraded to include an additional degree of freedom for scissors or gripper operation. There is room in the distal stage for a fourth driver pulley. The scissors mechanism would be attached to this fourth drive pulley, attached to a fourth tendon and driven by a fourth drive motor.
Fifteen (15) drawings are attached:
1. Outline view of the Tendon-Driven Serial Distal Stage.
2. Tendon routing path for pitch (first stage rotation).
3. Tendon routing path for yaw (second stage rotation).
4A. Tendon routing path for roll (third stage rotation): Sensors and brackets in place.
4B. Tendon routing path for roll (third stage rotation): Sensors and bracket removed.
5. Tendon routing path for tendon drive motor and tendon-tensioning assembly.
6A. Tendon-Driven Serial Distal Stage, with one embodiment of the Scissors Mechanism.
6B. Closer view of one embodiment of the Scissors Mechanism.
7. Overall view of the principal embodiment of the mechanism.
8. Roll and yaw mechanism, with roll tendon routing, showing enclosed Sensors 2 and 3.
9. Roll and yaw mechanism, with pitch tendon routing.
10. Roll mechanism, with roll tendon routing (from the underside of FIG. 9).
11. Distal mechanism, cut away to show sensors and bearings.
12. Closer view of distal mechanism cutaway.
13. Stylized view of distal mechanism.
14. Exploded stylized view of distal mechanism.